Hi all,
I have some Nikon BD Plan DIC objectives, which from my understanding after reading a post here on the forum, are no different than regular BD Plan objectives other than DIC can be used. I am wanting to know/test whether an APO lens will render clearer images when photographing coins (as well as things in slides), so I am wondering if I should get a BD or M plan for my APO lens.

What is the practical difference between M Plan and BD Plan objectives?

BD (Brightfield/Darkfield) objectives have a bundled DF condenser for reflected DF illumination, see: https://micro.magnet.fsu.edu/primer/techniques/darkfieldreflect.html
They are M objectives (M from Metallurgical, i.e. for use without cover glass). For BF work they are equivalent, often optically identical if the maker and time is the same.

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so I am wondering if I should get a BD or M plan for my APO lens.

I don't understand this, which apo lens are you referring to? Is it to be used as tube lens?_________________Pau